Signal that a field has become required after other user interaction

Question

The user is presented with a form. One of the form selections is a check box. If the user checks the check box, one of the fields is now required.

What is the best way to signal to the user that this is now a required field?

Answer 1

Its going to be hard to give a good answer unless I see your current form design but my suggestion would be to highlight that particular field so that the users eye is drawn to it (this is under the assumption that the field is always visible in the form and appears before the checkbox).

^{download bmml source – Wireframes created with Balsamiq Mockups}

Alternatively if you can hide the field , then you can show the field when the checkbox is selected and higlight it a little to draw user attention to it.

Answer 2

I would consider hiding the unnecessary fields until they're activated. It requires more coding, but it has at least two major advantages:

1. It removes visual clutter, simplifying and streamlining the experience
2. The dynamic movement attracts the eye -- which can be further enhanced by highlighting the new field in a different color

However, hiding fields has its own drawbacks. My experience has taught me that hiding important objects (e.g. submit buttons) until all the required fields are completed is a bad idea. Users may miss a field and panic when they don't see the function they're expecting. In such cases graying out the button (disabling) with an explanation that displays when the cursor is hovering over it makes more sense.

Perhaps the most important design decision in your case would be to place whatever fields become required in close proximity to the checkbox. Perhaps the required field could be hidden or minimized until the checkbox is selected. But it has to be close to whatever triggers it. That way the user will see the cause and effect and reflexively move to complete the field without having to be told that it is required. Hope that helps.